1. Field of the Invention
The present invention relates to a receiving paper for thermal transfer recording, which is used in combination with a thermal transfer recording medium including a thermofusible ink layer. Specifically the present invention relates to a receiving label for thermal transfer recording.
2. Discussion of the Related Art
Conventionally, various thermal transfer recording methods are known. For example, a method is proposed which uses a thermal transfer recording medium including a thermofusible ink layer and forming various information and images on labels such as papers and plastic films including an ink receiving layer. In particular, the thermal recording method is widely used for applications to an industrial field such that bar codes are printed by a thermal recording medium on a receiving material to be used for name plates, process control and logistic control. Since resistance to organic solvents, water, abrasion and chemical agents is required for the recorded images in the above-mentioned applications, plastic films such as polyester, polypropylene, polyethylene or synthetic papers are widely used as receiving materials. The thermal transfer recording medium for use for such applications typically includes an ink layer including a thermoplastic polymer as a main component so that the resultant images can resist the above-mentioned stresses and chemicals.
However, there is a problem in that plastic films used as receiving materials are expensive and therefore have a narrow range of applications. In addition, there is another problem in that labels using a natural fiber paper such as high quality papers or middle quality papers have poor ink receivability and fixability when a thermal transfer recording medium having an ink layer is used, which ink layer includes a thermoplastic polymer as a main component.
In contrast, for the purpose of improving the receivability of labels using a natural fiber paper as a substrate, many types of receiving materials have been proposed, which include an ink receiving layer having good thermofusible ink receivability on a substrate.
However, when these methods are used, resistance of the recorded images to organic solvents, abrasion and water is not satisfactory. In addition, when an adhesive layer is formed on the back surface of such a receiving material that is prepared by these methods to be used as a label, there is a problem in that because the substrate and the ink receiving layer do not have barriers against organic solvents and water, the adhesiveness of the adhesive layer on the back surface deteriorates due to the organic solvents and water, and thereby the label does not function as a label.
In contrast, published unexamined Japanese Patent Application No. 2001-199171 discloses a technology in which the binder resin in an ink layer and the binder resin used as main component of an ink receiving layer are of the same kind, and the SP value thereof are specified. In this technology, although recorded images have good resistance to organic solvents, abrasion and water, usability for users deteriorates because the ink and the receiving material have to be used as a combination and the range of applications thereof is extremely narrow.
In addition, published unexamined Japanese Patent Application No. H5-208562 proposes a provision of an intermediate layer having resistance to solvents between a substrate and an ink receiving layer using a polyvinyl alcohol having a degree of polymerization of from 50 to 450. In addition, published unexamined Japanese Patent Application No. H5-208563 proposes including an intermediate layer, which is formed of a polyvinyl alcohol having a hydrophobic group in an amount of from 18 to 80% by mole.
However, in the method in which an intermediate layer of a polyvinyl alcohol having a degree of polymerization of from 50 to 450 is used, the degree of polymerization is low, and therefore the film forming property is not satisfactory and the resistance to organic solvents is not satisfactory. In addition, since the materials used have high solubility to water, there is a problem in that when the materials are brought into contact with water, the intermediate layer dissolves and the layer is peeled off, resulting in that the receiving paper has poor water resistance. In addition, there is another problem in that since the intermediate layer has low polymerization, adhesiveness of the film is strong and the intermediate layer adheres to feeding rollers during coating, thereby decreasing productivity.
In addition, the method in which an intermediate layer of polyvinyl alcohol having a hydrophobic group in an amount of from 18 to 80% by mole is used has a drawback in that the higher the hydrophobic group content, the lower the resistance to organic solvents, and further, this method cannot provide a satisfactory resistance to organic solvents and water for the resultant images.
Because of these reasons, a need exists for an inexpensive label for thermal transfer recording on which images having good resistance to organic solvents, water and abrasion can be formed when the label is used as a label having a tackifying layer on the back surface thereof.